Wesley Clark, Nato Supreme Commander Europe said reconnaissance troops were "in the vicinity of Pristina airfield" while the armoured column was just 20 kms from the capital.

Paratroopers and Gurkhas rolled across from the neighbouring Former Yugoslav Republic of Macedonia, accompanied by French troops at first light on Saturday morning. For them it marked the culmination of three frustrating months of preparation and waiting.

A British soldier at the Kosovo border

The first British armoured cars crossed the border into Kosovo shortly after 0800 BST.

Spartan and Scimitar reconnaissance vehicles moved alongside the column and will be responsible for scouring the ground ahead of the armour when they go into Kosovo.

Four hours earlier wave after wave of Puma and Chinook helicopters flew low over the UK troops' Forward Assembly Area at Blace towards the high ground of southern Kosovo.

At the same time US Apache attack helicopters flew parallel with the British fleet across the border.

The first phase of Nato's deployment in Kosovo is now said to be complete.

(Click here to see an animated map showing timetable of Serb withdrawal and Nato's planned movements)

UK Armed Forced Minister Doug Henderson told the daily Ministry of Defence briefing in London that Nato troops advancing on Pristina faced a "perilous task" with hazards like mines and booby traps likely to be encountered along the way.

But the alliance says so far so good. Speaking via a live link from Skopje, the British commander in Macedonia, Major General Richard Dannert, said British forces had encountered elements of the Serb army and interior ministry police, as well as the KLA, but had met with no opposition.

The Nato operation appeared to be moving forward swiftly and UK Defence Secretary George Robertson praised the troops involved.

He said: "The signs of the professionalism and the training and the preparation are all coming together here.

"I am extremely pleased that we are now in there and that the troops of Nato will soon get to grips with creating a safe environment and we will then start to fulfil our promise to get those refugees home."